1. Field of the Invention
The present invention relates to an air bag system for an automotive vehicle and, more particularly, to an air bag system for an automotive vehicle so adapted as to protect in particular the passenger seated on the rear seat against impact of the automotive vehicle or a car crash.
2. Description of Related Art
Generally, there is known an air bag system in which an air bag unit is provided with an inflator and an air bag mounted in predetermined positions and it is so arranged as to protect the passenger seated in the vehicle compartment of the automotive vehicle against impact or shock acting upon a vehicle body of the automotive vehicle due to a car crash, etc. by rapidly expanding the air bag accommodated with the air bag unit in a folded or wound state by explosion of the inflator of the air bag unit.
U.S. Pat. No. 3,779,577 discloses an air bag system in particular for protecting the passenger seated on the rear seat, in which an air bag unit is mounted to a rear face portion of a seat back of each of left-hand and right-hand front seats.
The disposition of the air bag unit at the seat back of the front seat, however, poses the following problems.
1. The seat back of the front seat is located in many occasions in such a state that the rear face portion of the seat back is reclined obliquely downwards. Hence, the air bag mounted at the rear face portion of the seat back of the front seat is likely to be developed to expand in an obliquely downward direction, too, when a car crash has occurred, and the expanded air bag may not confine or protect particularly the head of the passenger seated on the rear seat in a sufficiently safe fashion.
2. It is difficult to set the air bag so as to expand always in an obliquely upward direction directed toward the head and chest portions of the passenger seated on the rear seat due to the correlation with a reclining angle of the seat back of the front seat.
3. When the air bag units should be exchanged, the whole portion of the seat back of the front seat is required to be exchanged so that expenses necessary for exchanges of the seat backs become extremely high.
Further, the disposition of the air bag unit at the front seat suffers from the disadvantage that a distance between the air bag unit and the passenger seated on the rear seat may become too long or too short to confine the passenger in an appropriate manner by expansion of the air bag mounted in the air bag unit, when a seat status or position of the front seat is changed, for example, when the front seat is slid and displaced forward.
Furthermore, a so-called submarine phenomenon should be taken into consideration when measures are taken to protect the passenger seated on the rear seat from the impact or shock due to a car crash. The so-called submarine phenomenon is intended herein to mean a phenomenon in which the leg portion of the passenger is caused to jump off a floor of the vehicle compartment, too, in accompaniment to the forward movement of the hip portion thereof upon a car crash.
If the submarine phenomenon would occur due to a car crash, the relationship of the position of the air bag unit with the posture or position of the passenger seated on the rear seat becomes so irregular that the passenger may not be confined by the expanded air bag in a sufficient way, thereby causing the passenger to jump off the rear seat.
It is further to be noted that the front seat is generally arranged to slide forward or backward, thereby permitting adjustment of the longitudinal direction of the front seat. The sliding mechanism is arranged that its front end portion becomes higher in its vertical position than its rear end portion, so that the front seat is inclined with its front end portion positioned higher than its rear end portion, as the front seat slides forward closer to a front end of the automotive vehicle. Thus, this arrangement for the longitudinally sliding mechanism for the front seat presents the problems that the passenger seated on the rear seat cannot be confined by expansion of the air bag due to a variation in the vertical position of the front seat, resulting in a variation in the direction in which the air bag is directed and expanded.